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Toutatis
2004-Apr-25, 10:33 AM
Kind friends

Below is linked an image of C/2004 F4 -- A composite of three, five-second frames. (Resolution = 1.25 arc seconds per pixel) - Credit: Juan Lacruz (With acknowledgments to Bill Allen [A/CC editor/publisher])

http://www.hohmanntransfer.com/mn/0404/24.htm

My question pertains to the appearance of a brilliant area at roughly the median of the tail... (To the right and at an angle of roughly 35 (Deg) UPward of the coma’s center as it appears in the image)

My best guesses

-The appearance of said ‘area’ is that of a background object (e.g. a star or planet) intensified via 'composition' of the frames?

-A region of increased 'tail density' owed to convergence of ejecta ‘jets’?

-Excitation of several adjacent charge-coupled 'cells' via incidental particulate radiation - or (non-optical) ionizing EMR???)

Hey folks - this is a [i]question not a quiz! :-) --- I am *hopeless* at observational astronomy, and as for image processing? - don't even ask http://www.rainbowpirates.com/forum/images/smiles/icon_redface.gif

Best regards
Sarandon

milli360
2004-Apr-25, 11:11 AM
My best guesses

-The appearance of said ‘area’ is that of a background object (e.g. a star or planet) intensified via 'composition' of the frames?
I'd imagine this is correct. It's not much brighter than the other stars that appear in the picture, and it has an elongation similar to theirs, and in the same direction. It is ineresting that it is brighter, and appears so close to the middle of the tail.

Kaptain K
2004-Apr-25, 02:13 PM
Looks like a star to me - Same orientation and elongation as other background objects.

lek
2004-Apr-25, 02:29 PM
Due to bad tracking ( or no tracking) the stars in the background are streched, with the star behind the tail the light of the tail is added to the stars brightness every moment of the exposure, so it seems lot brighter than the other stars.

(if that makes any sense :p)

Kaptain K
2004-Apr-25, 02:55 PM
Actually, it is good tracking - of the comet!

lek
2004-Apr-25, 03:01 PM
The amount of movement of the stars for those exposure times and magnification fits nicely in few seconds exposure without guidance.
The comet is just too diffuse to show signs of guidance error...
The comet isnt moving quite that fast relative to background.

Maksutov
2004-Apr-25, 09:04 PM
I contacted Mr. Lacruz about the setup used for the photograph and received this reply. The following is posted with his permission:

From: Juan Lacruz
Re: Comet Bradfield photograph


...I was tracking on the stars at the sidereal rate as usual.
The image is a composite, I averaged five frames 2 seconds each, when you do that on a fast moving object the stars result trailed.
But I noticed the oblong stars in the individual pictures, so this is not because of the comet's movement trailing the stars.
I also thought it could be bad periodic error correction due to tracking very off the meridian, but now I think this could most likely be an effect of atmospheric refraction.

Best regards,
Juan

This information clears up any question about tracking methods.

BTW, in our emails I included a link to the BA website. The response to this site was positive, thus we may have a new visitor/BABB member soon.

PhantomWolf
2004-Apr-25, 11:57 PM
It's an alien space ship hiding in the tail. ;)

darkdev
2004-Apr-26, 12:46 AM
Which reminds me...

Why do comets have tails? Why don't stars, moons, or planets? They're clipping through space too! Is it just the composition of the comet coupled with the lack of gravity to hold itself together, or does this only occur in the presence of mass radiation, like from our Sun? Both maybe?

I should probably already know this, but it would seem that there would need to be a counter-agent, (friction), in order to cause a tail/wake.

PhantomWolf
2004-Apr-26, 12:52 AM
They have tails because the materials that are in the nucleus of the comet sublime and then those gases are pushed away from the sun by the solar winds because the comet isn’t large enough to hold onto it through gravity. Planets don’t have them because they have enough gravity to hold their atmospheres together for the most part while their large magnetic fields add to the protection as well for the most part (some like Mars and Mercury don’t have that protection and so more of their atmosphere has been stripped.)

I have a feeling that BA actually has a page on this, I'll check and put it in if I can find it. ;)

[edited for link]

There's a bit here (http://www.badastronomy.com/mad/1997/hbtail.html)Though it related to Hale-Bop, I thought he had more somewhere but couldn't spot it. :(

darkdev
2004-Apr-26, 12:57 AM
That's cool, that's what I was thinking but wasn't sure; definately the right place to ask. =)

Kaptain K
2004-Apr-26, 06:44 AM
It's an alien space ship hiding in the tail. ;)
[ Rocket J. Squirrel voice] That trick never works! [/ Rocket J. Squirrel voice]

Maksutov
2004-Apr-26, 06:56 AM
It's an alien space ship hiding in the tail. ;)
[ Rocket J. Squirrel voice] That trick never works! [/ Rocket J. Squirrel voice]

Maybe so, but it was effective enough courtesy of Hale-Bopp to help clean out part of the gene pool (a la the Darwin Awards) in California. Just following their Fearless Leader, I guess. :roll:

The fine folks in Frostbite Falls probably wouldn't that easily tricked though. :)